[x3d-public] Beginner questions

[Joseph D Williams]

➢ > >as well as our "scene graph"

VRML/X3D uses a special sort of scenegraph called a DAG. 
This is important for x3d, notice how DEF/USE works. 

Joe

From: Michalis Kamburelis
Sent: Thursday, January 17, 2019 12:56 AM
To: iam here
Cc: X3D Graphics public mailing list
Subject: Re: [x3d-public] Beginner questions

iam here <iamhereintheworld at gmail.com> wrote:
>
> Michalis Kamburelis said:
> >as well as our "scene graph"
>
> OK, I don't know what a "scene graph" is, but....does it have something to do with Graph Theory, as taught in Computer Science?

X3D represents 100% of the scene as a graph of nodes: you have a
"Transform" node, and as children it can have other "Transform" nodes,
or a "Shape" node, or many others. It is usually a simple tree (a
special case of a graph, probably the simplest one), but sometimes
it's more complicated (due to DEF / USE in X3D).

This concept is actually present in most (if not all?) of 3D APIs and
3D model formats.
- glTF also has a transformation hierarchy, which is a tree of
transformation nodes, IOW also a graph.
- Unity has a transformation hierarchy which is a tree of GameObject instances.
- Castle Game Engine exposes a graph of X3D nodes to the programmer
(and we also have a tree of TCastleTransform instances).

Yes, the term "graph" means here the same thing as "graphs" they talk
about in the "Graph Theory" course :) But you don't really to know any
advanced theory to understand it. A graph is a set of "things"
(nodes), and some of those things are connected. That's it, in a
nutshell :)

Regards,
Michalis

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